Multiple layered hoses including hoses, which contain foamed and non-foamed layers, are known in the art. For example, U.S. Pat No. 4,644,977 to Arterburn discloses a reinforced lightweight, flexible hose which comprises a two-component tube consisting of a thin, non-foamed inner liner and a foamed interlayer circumferentially encompassing the inner liner; a separate of textile reinforcement telescoped over the two-component tube; and a two-component, coextruded, thermoplastic outer cover layer circumferentially encompassing the reinforced tube, wherein the two-component coextruded thermoplastic outer cover includes a first thermoplastic layer with a multitude of closed gas-filled cells and a second thermoplastic layer which is non-foamed. The second, non-foamed thermoplastic layer has a thickness of from 15% to 73% of the thickness of the first thermoplastic layer and forms the outer surface of the hose. The coextruded first and second thermoplastic layers are specifically characterized as being free of any intervening material.
The present invention relates to tubular structures and particularly to flexible tubular structures such as coolant hoses for use in the automotive industry, and to the manufacture of such tubular structures.
Tubular structures, in general, are constructed from various polymeric materials such as chlorinated polyethylene (CPE); chlorosulfonated polyethylene (CSM); natural rubber; synthetic rubber such as ethylene acrylic copolymer (AEM), styrene-butadiene rubber (SBR), neoprene, ethylene-propylene rubber (EPR), butyl rubber, polybutadiene, polyisoprene, nitrile-butadiene rubber (NBR) polybutylene, ethylene-propylene diene terpolymers (EPDM) and the like; blends of such natural and synthetic rubbers; vulcanizable blends of natural and synthetic rubber; blends of natural and/or synthetic rubbers with. e.g., vinyl resins; and thermoplastic materials such as polyolefins, polyurethanes, etc.
Generally, in order to provide sufficient strength and stability to hoses manufactured from such materials, the manufacturer has to apply a reinforcing layer between the inner tubular structure and the cover layer. For example, U.S. Pat. No. 3,547,162 to Schaerer teaches a synthetic plastic pipe embedded in a rigid building material for use as a water conduit, particular for transporting hot water, wherein the plastic pipe includes an inner crosslinked olefinic polymer; an intermediate reinforcing layer comprising a braided jacket of natural, semi-synthetic or synthetic fibers; and an outer layer of synthetic plastic foam surrounding the intermediate reinforcing layer. The application of the reinforcement greatly increases the complexity of the manufacture process by requiring a separate manufacturing step wherein the inner tubular structure of the hose is cooled in order to apply the reinforcing material and then heated up again before extruding any subsequent layers, resulting in decreased production rates.
Furthermore, specialized machinery, which takes up a considerable amount of critical space, is required to apply the reinforcement. Such machinery requires regular maintenance and needs to be shut down periodically to replenish the reinforcement material. The use of short reinforcement fibers or particles generally overcomes the above problems of needing additional machinery, but the short reinforcement fibers or particles have a tendency to align themselves in a longitudinal direction during conventional extrusion. While the short fibers and/or particles within an extruded bed of material increases the longitudinal strength of the material, they contribute very little to the radial strength of the tube. Therefore, it is a primary object of the present invention to provide a flexible reinforced hose, which has improved radial strength as well as acceptable longitudinal strength to meet the requirements of the automotive industry. It is another object of the invention to provide a reinforced hose, which is more economical and faster to manufacture than previous hoses. It is still another object of the invention to provide a method for manufacturing such flexible reinforced hose without the need for additional equipment, which requires further process steps.